A&P - General Oral Exam (8083)

What constitutes a capacitor?

Two conductors separated by an insulator.

What is the purpose of a capacitor?

It stores electrical energy in electrostatic fields.

Does a capacitor in an AC circuit cause the current to lead or lag the voltage?

It causes the current to lead the voltage.

What is the basic unit of capacitance?

The ferad.

Why should electrolytic capacitors not be used in an AC circuit?

They are polarized. An electrolytic capacitor will pass current of one polarity, but will block current of the opposite polarity.

What is meant by inductance?

The ability to store electrical energy in electromagnetic fields.

What is the basic unit of inductance?

The henry.

What is an example of an inductor used in a magneto?

The coil.

Does an inductor in an AC circuit cause the current to lead or lag the voltage?

It causes the current to lag behind the voltage.

How can you find the polarity of an electromagnet?

Hold the electromagnet in your left hand with your fingers encircling the coil in the direction electrons flow (from negative to positive). Your thumb will point to the north pole of the electromagnet.

What is meant by impedance?

The total opposition to the flow of alternating current. It is the vector sum of resistance capacitive reactance, and inductive reactance.

In what units is impedance measured?

In ohms.

What are five sources of electrical energy?

Magnetism, chemical energy, light, heat, and pressure.

What is the basic unit of power in a DC circuit?

The watt.

What is meant by a kilowatt?

1,000 watts.

What is meant by a megawatt?

1,000,000 watts.

What is the formula for power in a DC circuit?

Power \= Voltage times current (P \= E x I)

What is the relationship between mechanical and electrical power?

1 horsepower \= 746 watts

What is meant by true power in an AC circuit?

The product of the circuit voltage and the current that is in phase with this voltage.

In what units is true power expressed?

In watts.

What is meant by apparent power in an AC circuit?

The product of the circuit voltage and the circuit current.

In what units is apparent power expressed?

In volt-amps.

What is meant by the reactive power in an AC circuit?

The power consumed in the inductive and capacitive reactances in an AC circuit. Reactive power is also called wattless power.

In what units is reactive power expressed?

In volt-amps reactive (VAR), or kilovolt-amps reactive (KVAR).

What is meant by power factor in an AC circuit?

The ratio of true power to apparent power. It is also the ratio of circuit resistance to circuit impedance.

Which law of electricity is the most important for an aircraft mechanic to know?

Ohm's law.

What are the elements of Ohm's law?

Voltage E, current I, and resistance R (volts, amps, and ohms).

What is voltage?

Electrical pressure.

What is the basic unit of voltage?

The volt.

What instrument is used to measure voltage?

A voltmeter.

To measure voltage, is a voltmeter placed in series or in parallel with the source of voltage?

In parallel.

What is electrical current?

The flow of electrons in a circuit.

What is the basic unit of current flow?

The ampere (amp).

What part of an amp is a milliamp?

One thousandth (0.001) of an amp.

What instrument is used to measure current flow?

An ammeter.

What two things happen when current flows through a conductor?

Head is generated and a magnetic field surrounds the conductor.

To measure current through a component, is an ammeter placed in parallel or in series with the component?

In series.

What is meant by resistance in an electrical circuit?

The opposition to the flow of electrons.

What is the basic unit of electrical resistance?

The ohm.

What is a megohm?

One million (1,000,000) ohms.

What four things affect the resistance of an electrical conductor?

The material, the cross-sectional area, the length, and the temperature.

What instrument is used to measure electrical resistance?

An ohmmeter.

How can you tell the resistance of a composition resistor?

By a series of colored bands around one end of the resistor.

What is meant by continuity in an electrical circuit?

The circuit is continuous (or complete) when electrons can flow from one terminal of the power source to the other.

What instrument is used to measure continuity in an electrical circuit?

An ohmmeter.

When measuring resistance of a component with an ohmmeter, should the circuit be energized?

No, there should be no power on the circuit.

What three things must an electric circuit contain?

A source of electrical energy, a load to use the energy, and conductors to join the source and the load.

What are three types of DC circuits with regard to the placement of various circuit components?

Series, parallel, and series-parallel.

What is the name of the law that describes the relationship in electrical circuit of voltage, current and resistance?

Ohm's law.

What is the basic equation of Ohm's law?

E \= I x R

What formula is used to find current when voltage and resistance are known?

I \= E/R

What formula is used to find resistance when voltage and current are known?

R \= E/I

What happens to the current in a DC circuit if the voltage is increased but the resistance remains the same?

It increases.

What happens to the current in a conductor if the length of the conductor is doubled with all other parameters unchanged?

It would decrease to one half.

What is the voltage across each resistor connected in parallel across a 12-volt battery?

12 volts.

How much current flows through each of three resistors connected in a series if the total current is 3 amps?

3 amps.

What is the total resistance of three 12-ohm resistors connected in series?

36 ohms.

What is the total resistance of three 12-ohm resistors connected in parallel?

4 ohms.

What is meant by the capacity rating of a lead-acid battery?

The number of hours a battery can supply a given current flow.

In what units is battery capacity expressed?

In ampere-hours.

What electrolyte is used in a lead-acid battery?

A mixture of sulfuric acid and water.

Does the specific gravity of the electrolyte in a lead-acid battery increase or decrease as the battery becomes discharged?

It decreases.

What is the specific gravity of a fully charged lead-acid battery?

Between 1.275 and 1.300.

How many cells are there n a 24-volt lead-acid battery?

12

What is the range of temperatures of the electrolyte in a lead-acid battery that does not required a correction when measuring its specific gravity?

Between 70°F and 90°F.

What instrument is used to measure the specific gravity of the electrolyte in a lead-acid battery?

A hydrometer.

How do you treat a lead-acid battery compartment to protect it from corrosion?

Paint it with an asphaltic (tar-base) paint or with a polyurethane enamel.

What is used to neutralize spilled electrolyte from a lead-acid battery?

A solution of bicarbonate of soda and water.

How high should the electrolyte level be in a properly service lead-acid battery?

Only up to the level of the indicator in the cell.

Why is the closed-circuit voltage of a lead-acid battery lower than its open-circuit voltage?

Voltage is dropped across he internal resistance of the battery.

What is the open-circuit voltage of a lead-acid cell?

2.1 volts.

What gases are released when a lead-acid battery is being charged?

Hydrogen and oxygen.

What precautions should be taken in the maintenance ship where both lead-acid and nickel-cadmium batteries are serviced?

The two types of batteries should be kept separate, and the tools used on one type should not be used on the other.

What is the electrolyte used in a nickel-cadmium battery?

Potassium hydroxide and water.

Why is a hydrometer not used to measure the state of charge of a nickel-cadmium battery?

The electrolyte of a nickel-cadmium battery does not enter into the chemical changes hat occur when the battery is charged or discharged. Its specific gravity does not change appreciably.

Is the electrolyte level of a nickel-cadmium battery lowest when the battery is fully charged or fully discharged?

Fully discharged.

What is the result of cell imbalance in a nickel-cadmium battery?

The low internal resistance allows current to flow between the unbalanced cells and generate heat.

What is the thermal runaway?

The large current flow allowed by the low internal resistance causes the middle cells to produce more heat than they can dissipate. The heat further lowers the internal resistance so more current can flow; this continues until the battery destroys itself.

How may thermal runaway be prevented?

By carefully monitoring the temperature of the middle cells and controlling the charging current to prevent an excess of current flowing into the battery.

How is it possible to know when a nickel-cadmium battery is fully charged?

Completely discharge the battery and give it a constant-current charge to 140% of its ampere-hour capacity.

What is used to neutralize spilled electrolyte from nickel-cadmium battery?

A solution of boric acid and water.

How many views can there be on an orthographic projection?

Six.

How many views are used to show most objects in an aircraft drawing?

Three.

What information is given in the title block of an aircraft drawing?

The name and address of the company who made the part, the name of the part, the scale of the drawing, the name of the draftsman, the name of the engineer approving the part, and the number of the part (the drawing number).

Where is the title block normally located on an aircraft drawing?

In the lower right-hand corner of the drawing.

How can you know that the aircraft drawing you are using is the most current version of the drawing?

By the number in the revision block, and by the log of the most recent drawings.

What is a fuselage station number?

The distance in inches from the datum, measured along the longitudinal axis of the fuselage.

What is a butt line?

A reference line to the right or left of the center line of the aircraft.

What is a detail drawing?

A drawing that includes all the information needed to fabricate the part.

What is an assembly drawing?

A drawing that shows all the components of a part in an exploded form. A parts list is included with an assembly drawing.

What is an installation drawing?

A drawing that shows the location of the parts and assemblies on the complete aircraft.

What type of drawing is most helpful in troubleshooting a system?

A schematic diagram.

What is a block diagram?

A drawing that shows the various functions of a system by a series of blocks. These blocks do not include any detail, but instead indicate what happens in each block.

How are dimensions shown on an aircraft drawing?

By numbers shown in the break of a dimension line.

What is the purpose of a sketch of a repair?

It shows a specific bit of information and includes the minimum amount of detail needed to manufacture the part.

What are the four steps in making a sketch?

Block in the space and basic shape used for the sketch.
Add details to the basic block.
Darken lines that are to show up as visible lines in the finished sketch.
Add dimensions and any other information that will make the sketch more usable.

What is the purpose of a center line on an aircraft drawing?

It divides a part into symmetrical halves.

When should an aircraft be reweighed?

After an extensive repair or alteration that could change its weight or center of gravity.

Why is it necessary to consider the category under which an aircraft is licensed when computing its weight and balance?

Different categories under which an aircraft can be licensed have different maximum gross weights and different center of gravity ranges.

Where do you find the leveling means that are specified for a particular aircraft?

In the Type Certificate Data Sheets for the aircraft.